1. Field of the Invention
The present invention relates to a zoom lens and an image pickup device including the same, and is suitable to, for instance, a video camera, a digital still camera, a monitoring camera, a TV camera, and a silver halide photography camera.
2. Description of the Related Art
An imaging optical system included in an image pickup device requires a high zoom ratio, a high optical performance over the entire zoom range, a small size, and a small thickness in the direction of the front and rear of the camera. To reduce the thickness of the camera, a folded zoom lens has been known in which a reflection unit (one of a mirror member and a prism member) that bends the optical axis of an imaging optical system by 90° is arranged on the light path.
Japanese Patent Application Laid-Open No. H10-020191 discloses a zoom lens that includes, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power. In this zoom lens, the second lens unit and the fourth lens unit move during zooming, and a reflection unit that bends the light path is arranged between the third lens unit and the fourth lens unit.
Japanese Patent Application Laid-Open No. 2007-279541 discloses a zoom lens that includes, in order from an object side to an image side: a first lens unit having positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power. In this zoom lens, the first lens unit and the third lens unit move during zooming, and a reflection unit for bending the light path is arranged between the second lens unit and the third lens unit.
Japanese Patent Application Laid-Open No. 2008-191291 discloses a zoom lens that includes, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; a fourth lens unit having a negative refractive power; and a fifth lens unit having a positive refractive power. This zoom lens is provided with a reflection unit that bends the light path in one of the first lens unit and the second lens unit.
To achieve a zoom lens that allows the thickness of a camera to be reduced and has a high optical performance over the entire zoom range while achieving a high zoom ratio, it is important to appropriately set the position of the reflection unit in the light path, the lens configuration of the zoom lens, and the refractive power and moving conditions of a variable magnification lens unit.
Conventionally, in many folded zoom lenses, to reduce the thickness of the camera, the reflection unit is arranged on the front side of the lens system (the side near the object). Thus, the dimension in the depth direction of the lens system can be reduced. However, a large space for accommodating a plurality of lens units including a moving lens unit is required in a direction perpendicular to the incident optical axis into the lens system after the reflection unit (image side). It is thus difficult to apply the configuration to an image pickup device having a configuration in which a sufficient space is difficult to be secured.
As such an image pickup device, for instance, a video camera has been known which is held in a state where a palm stands and the fingers wrap the camera. Another example is a monitoring camera including a lens barrel accommodated in a common chassis having a shape like a rectangular parallelepiped for allowing a housing and a pan-tilt drive mechanism to be commonly used among lenses having different specifications.
Thus, to allow a folded zoom lens to be applied to various image pickup devices, and to reduce the thickness in the case of application to a camera, it is important to appropriately select a zoom type and set the position of reflection unit on the light path. If these configurations are inappropriate, various aberrations largely vary during zooming, and it is difficult to achieve a high zoom ratio and reduce the thickness of the entire lens system.